In cellular systems such as LTE (Long Term Evolution) and WiMAX (Worldwide Interoperability for Microwave Access), a terminal performs wireless communication with a base station. Usually, since one base station communicates with a plurality of terminals, the base station performs scheduling for dynamically allocating finite communication capacity (resource) to each terminal so as to prevent interference of signals between the terminals. When uplink communication in the LTE is taken as an example, a sequence from when a terminal (UE: User Equipment) as a wireless terminal generates uplink data to when the terminal transmits the data to a base station (eNB) is as shown in FIG. 1. First, when UE 92 requests bandwidth from eNB 91, the eNB 91 obtains information (such as an amount of buffer data and a channel state) required for scheduling of the uplink data, therefore the eNB 91 allocates a resource for transmitting those information to the UE 92, and gives notice to the UE 92 by returning a response.
When the UE 92 transmits the information, required for scheduling the uplink data in the allocated resource, to the eNB 91, the eNB 91 performs scheduling and allocates the resource for transmitting the uplink data to the UE 92 using a scheduling grant. The UE 92 can transmit the uplink data to the eNB 91 only after these exchanges. In the downlink communication, since the number of the base station transmitting a signal is one, interference does not occur, and thus the exchanges before communication between the UE 92 and eNB 91 are not usually performed.
In a cellular system, in order to enhance the degree of freedom of cell configuration, the function of the eNB 91 is divided into a base band signal processing unit (BBU: Base Band Unit) 81 and an RF signal transmitting/receiving unit (RRH: Remote Radio Head) 83, whereby physically separated configuration can be achieved. Although a radio signal between the BBU 81 and the RRH 83 can be transmitted through an optical fiber by an RoF (Radio over Fiber) technique, recently, a digital RoF technique excellent in transmission quality compared with an analogue RoF technique has been particularly actively studied, and use formulation has been progressed under a standards body such as CPRI (Common Public Radio Interface) (see, for example Non Patent Literature 1).
As a connection form between the BBU 81 and the RRH 83, a point-to-multipoint form utilizing a PON (Passive Optical Network) system can be taken. In this case, as shown in FIG. 2, the BBU 81 and the RRH 83 are connected to each other by optical fibers and an optical splitter 84. In PON, since OLT (Optical Line Terminal) 10 as an single terminal station device communicates with ONUs (Optical Network Units) 82 as a plurality of subscriber devices in its nature, the OLT 10 performs scheduling for dynamically allocating capacity to the ONUs 82.
A sequence until the ONU 82 transmits uplink data to the OLT 10 in normal PON is shown in FIG. 3. As in the LTE, although the scheduling on the OLT 10 side requires information (REPORT) such as an amount of data buffered in the ONU 82, the REPORT can be transmitted only at a timing allocated by a transmission permission signal transmitted from the OLT 10. The OLT 10 performs scheduling based on REPORT information, allocates a resource for transmitting the uplink data to the ONU 82, and notifies the ONU 82 of this through GATE. The ONU 82 can transmit the uplink data to the OLT 10 only after these exchanges. In the downlink communication, the exchanges before communication between the OLT 10 and the ONU 82 are not particularly performed.
In a system shown in FIG. 2, the system is in a state in which schedulers of two systems, that is, a cellular and PON are mixed in a single system, and, for example, a sequence of uplink communication from the UE 92 becomes as shown in FIG. 4 based on FIGS. 1 and 3. In this case, the bandwidth requirement or the notification of the amount of buffer data before sending uplink data transmitted from the UE 92 cannot be transmitted without going through all sequences of the uplink communication of the PON.
Meanwhile, in order to save power consumption of the device, the cellular system and the PON may have a function of pausing some devices on the side where a plurality of devices exist during a time when communication is not performed. Regardless of a system, a transmitting side usually enters a pause state when a transmission data amount is small and is recovered from the pause state when transmission data is generated. In a receiving side, since data to be received may exist while the receiving side pauses, the receiving side is often set to recover from the pause state at fixed intervals of time and confirm the existence of the data to be received.
As an example of the above, in discontinuous reception of the LTE, a sequence from a normal receiving state to start of the discontinuous reception and a sequence to termination of the discontinuous reception are shown in FIGS. 5 and 6, respectively. The UE 92 starts the discontinuous reception when a resource is not allocated if a constant time T1 or more is elapsed from the latest allocation of a radio resource to the UE 92 (FIG. 5). When the UE 92 is in an discontinuous reception state, the UE 92 repeats such an operation that some devices relating to reception are paused only for a time T2 and recover from the pause state for a time T3. When it is detected that a resource for downlink communication is allocated within the time T3 when the UE 92 is in a recover state, the UE 92 recovers from the discontinuous reception state (FIG. 6). Although cyclic parameters of T1 to T3 for the discontinuous reception is designated by the eNB 91 during connection, there is no particular regulation on notification from the UE 92 to the eNB 91 before the UE 92 enters the discontinuous reception state, and the operation can be performed as an independent operation on the terminal side.
Meanwhile, a control message and a state transition diagram for realizing sleep of the ONU 82 in the PON are prescribed by ITU-T G.987.3 (see, for example Non Patent Literature 2). Messages such as Sleep Allow (ON) for which the OLT 10 allows each of the ONUs 82 to sleep, Sleep Allow (OFF) for which the OLT 10 forbids each of the ONUs 82 to sleep, Sleep Request (Sleep) for which the ONU 82 requires the OLT 10 to sleep, and Sleep Request (Awake) for which the ONU 82 requires the OLT 10 to awake are specified.
PON sleep based on G.987.3 is different from the discontinuous reception of the LTE in that the OLT 10 manages a sleep state of the ONU 82. An example of a procedure until sleep is started and an example of a procedure until the sleep state shifts to an active state are shown in FIGS. 7 and 8, respectively. When the OLT 10 does not detect a downlink frame addressed to the relevant ONU 82 only for a fixed time T4, the Sleep Allow (ON) is transmitted from the OLT 10 to the ONU 82, and the ONU 82 transmits the Sleep Request (Sleep) to the OLT 10 and enters the sleep state (FIG. 7). The sleep is cyclic as with the discontinuous reception of the LTE, and the ONU 82 repeats such an operation that the ONU 82 maintains the sleep state only for a time T5 and then recovers only for a time T6. Before the ONU 82 shifts from the sleep state to the active state, the ONU 82 receives the Sleep Allow (OFF) from the OLT 10 within the time T6 and returns the Sleep Request (Awake) (FIG. 8). The ONU 82 receives a frame addressed to the ONU 82 itself after shifting to the active state.
When the LTE and the PON each have such functions including the discontinuous reception and the sleep as described above, in a system in which they are combined as shown in FIG. 2, each system can pause a portion of a device. In the system as shown in FIG. 2, a sequence to start of the sleep of the PON when the discontinuous reception and sleep control of each of the LTE and the PON are independently operated is shown in FIGS. 9 and 10. FIGS. 9 and 10 show, respectively, a case where the last traffic before shifting to the discontinuous reception and the sleep state is downlink data and a case where the last traffic is uplink data. For both the cases, while in the LTE the UE 92 shifts to the discontinuous reception once a time T1 has elapsed from the last traffic, in the PON the OLT 10 transmits the Sleep Allow (ON) to the ONU 82 once the time T4 has elapsed from the last traffic, and the ONU 82 shifts to the sleep state.